This paper presents a general description of the xero-graphic photoreceptor and its role in the imaging process. The photoreceptor is described in terms of two properties, the photoinduced charge-generation efficiency and the charge transport through the bulk of the material. The relationships between these fundamental photoreceptor properties and the final electrostatic imaging system are present...

The dark-discharge rate of corona-charged amorphous films of As2Se3 is dependent upon the electric field, temperature, and the duration of discharge. The dark-discharge current was found to result from both bulk generation of holes and from surface injection of holes. Negative charges are immobile in the material. The surface contribution gradually diminishes over a period of weeks as the film ages, or it can be eliminated by applying a thin organic insulating layer to the photoconductor surface. The bulk generation contribution, identified by its linear dependence upon film thickness, is the subject of more detailed analysis. The discharge rate increases slightly at higher electric fields. During the period of a single discharge measurement, the rate drops faster than can be explained by the field dependence. In addition, the discharge rate increases rapidly with temperature. There is no unique activation energy characterizing the discharge process. To account for the discharge time and temperature dependencies, two sets of generation centers are postulated to lie within the band gap of the material. The first set lies 0.6–0.78 eV above the hole conduction states and the density of centers at each energy increases slowly with increasing energy. The second set is located at 0.8–0.86 eV above the hole conduction states, whose density is more than 2 orders of magnitude greater than that of the shallower centers. A first-order kinetic mechanism is assumed for the hole generation from each energy level. The density of the first set of centers has been calculated to be 1014 cm−3 and the second set is in the range 1016−1017 cm−3. A Poole-Frenkel type of relationship is used to correlate the electric field dependency of the dark-discharge rate. Using this model, the surface potential can be predicted as a function of the discharge time, the temperature, and the initial field, provided no severe internal field distortion exists in the bulk of the photoconductor.

Electromagnetic radiation approximately equal to band-gap energy has been established as responsible for the dissociation of amorphous As2Se3 and As2S3. The dissociation is accompanied by an optical densification observable as a ``photographic'' effect in thin films of these materials. The dissociation can be expressed by the following equations: As2Se3→ lim hvxAs+As2−xSe3, 0

Charge transport and photoconductivity in As2S3 amorphous films have been investigated at a temperature of 25°C. It is found that holes are the mobile carriers in As2S3 whereas electrons are quite immobile in the material. The photoconductivity is mainly governed by the product of the photogeneration efficiency and the schubweg of the generated holes. Both of these quantities are electric field dependent. Carrier transport is essentially dominated by bulk trapping. The traps are distributed in energies above the hole conduction states. The release rate of the trapped charges varies since the rate is an inverse function of the trap energy. A theoretical model describing the transport process is presented to account for the experimental results. The photogeneration efficiency as a function of electric field at high fields (greater than 105 V/cm) has been determined for incident photon energies of 2.5–3.1 eV. The generation efficiency is observed to decrease in the same manner as the absorption coefficient with decreasing photon energy in the light wavelength range 4000–5000 Å.

Adhesion of evaporated amorphous Se on oxide surfaces has been studied. For selenium evaporated in a relatively poor vacuum of 10−5 Torr onto aluminum substrates coated with a surface oxide layer, the Se deposit could easily be peeled off the substrate. Electron microscope examination of the separated surfaces showed that the separation, in general, occurred at or in the immediate vicinity of the Se-aluminum oxide interface. Complimentary studies were also conducted on Se evaporated onto oxide substrates in an ultra-high vacuum system. Substrates used were single crystals of sapphire and MgO and virteous quartz. Experimental observations indicated that the relative strength of adhesion and the fractured surface features were dependent on and could be correlated with the substrate preheat temperaure in a high vacuum prior to Se evaporation. With a sufficiently high preheat temperature, the interfacial bond strength exceeded that of the cohesive energy of Se and the failure occurred in the Se layer. Studies on the effect of chemisorbed gas species on adhesion showed that water absorption does not degrade the strength of the Se-oxide structure. However, absorption of long chain organic acids and alcohols on the substrate surface resutled in poor adhesion strength, and the failure occurred at the interface region.

AbstractInterfaces of evaporated viterous selenium and various organic polymeric resins of both the thermosetting and thermoplastic type have been studied by ultra‐thin sectioning and transmission electron microscopy techniques. Epoxy, phenoxy, polyamide, butadien–styrene copolymer, vinyl‐toluene–butadiene copolymer, resins as well as polyethylene are among those organic polymers studied. Interfaces prepared by vaccum evaporation of selenium onto the various substrates and under varying processing conditions were examined. Intermixing and interdiffusion of the inorganic and organic polymers in the interfacial region were observed in certain cases when selenium was evaporated onto incompletely curved epoxy or lower viscosity polymers. These occurrences were found to contribute significantly to the mechanical strength of the assembly. Electrical properties of certain specific systems have also been investigated.

Surface dye sensitization of amorphous Se has been studied. Maximum quantum efficiencies measured were in the range from 10−2 to 10−1. The dye coatings were deposited onto the surfaces from their respective methanol or benzene solutions. Five dyes were used for the sensitization: crystal violet, pinacyanole, methylene blue, phenosafranine, and nitrosobenzene. The enhanced photocurrents due to the dye coatings occured at wavelengths longer than those corresponding to the intrinsic bandgap energies of Se. The maximum enhanced response was in the range from 5500 to 7000 Å, depending on the dye. The enhanced photocurrents corresponded to injection of carriers from the surface into the bulk photoconductor, electrons for some dyes (crystal violet and pinacyanole) and holes for others (methylene blue, phenosafranine, and nitrosobenzene).

Surface dye sensitization of polycrystalline orthorhombic sulfur has been observed. The dyes used for the sensitization were rhodamine B and pinacyanole. Maximum enhanced photoresponse occurred in the wavelengths from 4500 to 6000 Å. Quantum efficiencies up to slightly over 10−2 have been measured. The observed photocurrents corresponded to electron injection from the sulfur—dye interface into the sulfur.

A process is described for the formation of silicon oxide thin films by the low‐temperature decomposition of tetraethoxysilane in an a‐c glow discharge. The effects of various process parameters on the film deposition rate and the resultant film characteristics have been studied and are described. It has been shown that thin silicon oxide films prepared by glow discharge techniques can be used effectively as the dielectric in thin film capacitors. The resultant capacitors have low dielectric losses and are very stable under various life test conditions.

Experimental studies are presented in which reverse leakage currents in diffused silicon planar diodes are reduced by orders of magnitude via an intermediate temperature (800°–1000°C) gettering of metallic impurities which presumably cause excess leakage. Inorganic oxides having melting points below the gettering process temperature have been employed as the getters. Life test data on gettered diodes are also presented. The effectiveness of such gettering processes is further demonstrated by experiments in which radioactive copper is utilized as the diffused contaminant.